The present invention relates to an ink-jet recorder that produces bubbles in ink retained in a nozzle and squirts the ink by application of energy which heats heat-generating elements provided in the nozzle.
Much attention is now focused on ink-jet recording systems. The ink-jet recording system has a superior balance of recording quality, recording speed, and costs. Further, the ink-jet recording system has several advantages; ease of production of colored prints, capability of recording information on ordinary paper, and its silent operation. There have not been any instances of a continuous recording system, which selectively impacts ink being continuously squirted onto paper, since 1985. Instead of the continuous recording system, a drop-on-demand recording system, which selectively squirts ink, has become dominant. With regard to the drop-on-demand recording system, there are thermal (bubble) recording systems which squirt ink by use of bubbles resulting from rapid heating of ink, and piezoelectric recording systems that squirt ink using ceramics which become deformed upon receiving an applied voltage.
In the case of a thermal ink-jet recording system, through the use of thermal energy the temperature of the recording system increases during recording operations. An increase in the temperature of ink results in a decrease in the viscosity of the ink, so that the amount of ink droplet that is squirted increases. For this reason, variations in the temperature of the recording system result in changes in the amount of ink droplet that is squirted, thereby resulting in deterioration of the print image.
To prevent such a problem, a technique for maintaining a constant amount of ink droplets to be squirted regardless of variations in the temperature of the recording system, is disclosed in the Unexamined Japanese Patent Application Publication No. Hei 5-31906. According to this technique, heat-generating elements are not driven by a single pulse, but by two pulses; namely, a pre-pulse and a main pulse. The width of the pre-pulse is varied according to the temperature of the heat-generating elements. Compared with the case where the heat-generating elements are driven by a single pulse, superior energy efficiency is achieved in the case where the heat-generating elements are driven using double pulses; i.e., a pre-pulse and a main pulse. Further, the volume of foam and squirting speed can be controlled easily by using the double pulses.
As disclosed in; e.g., the Unexamined Japanese Patent Application Publication No. Hei 7-96607, a technique has been recently developed for improving drive frequencies by inserting a pulse for driving another heat-generating element into the interval between the pre-pulse and the main pulse for driving an identical heat-generating element, when the heat-generating element is driven using double pulses. If it is also possible to drive the heat-generating element using a single pulse in the form of an input signal sequence, the print speed can be further increased.
The maximum number of dots which can be simultaneously printed by the thermal ink-jet recording system is determined by several constraints; namely, the capacity of power and a voltage drop due to the resistance of wiring, and interaction occurring between ink pressures. For instance, provided that heat-generating elements which permit passage of an electrical current of about 200 mA is used, an electrical current of more than 1A flows at one time provided that more than five heat-generating elements are driven at the same time. If a large electrical current flows through the center of a board having the heat-generating elements mounted thereon, a voltage drop develops in a common electrode, which adversely affects printing operations. Further, there is a risk of noise mixing into a print head or into a common flexible cable connecting a printer main unit to the print head, as a result of rapid flow of a large electrical current, which in turn adversely affects the printing operations.
In contrast, in order to realize cost reductions and high-density packaging, a method has been proposed wherein a drive circuit for controlling a driver, as well as the driver, are mounted on an identical silicon board having heat-generating elements mounted thereon. As disclosed in; e.g., in the Unexamined Japanese Patent Application Publication No. Hei 7-76078, a recent apparatus has means for driving heat-generating elements, which are divided into groups of a certain number of heat-generating elements, in a time-sharing manner. A block to be driven is designated by a decoder using a decode signal, so that the number of wires is reduced.
To reduce the interaction which occurs between heat-generating elements at the time of ink-squirting operations, a technique has been proposed as disclosed in; e.g., the Unexamined Japanese Patent Application Publication No. Hei 6-191039, in which all the adjoining heat-generating elements are divided into blocks of a certain number of heat-generating elements, and the blocks which are spaced as far away as possible are sequentially driven without driving the adjoining blocks when the blocks of the heat-generating elements are driven in a time-sharing manner. Further, the Unexamined Japanese Patent Application Publication No. Hei 6-198893 discloses a technique in which all of the adjoining heat-generating elements are divided into four blocks every three heat-generating elements, and the thus-divided heat-generating elements are driven in a time-sharing manner. More specifically, according to the technique disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-191039, the heat-generating elements which are adjoined in each block, and the blocks of the heat-generating elements are discretely driven. In contrast, according to the technique disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-198893, the heat-generating elements are separately arranged every three elements within each block, and the adjoining blocks of the heat-generating elements are sequentially driven. As described above, techniques regarding drive executed on a block-by-block basis are put forward, as well.
FIG. 34 is a circuit diagram of a substrate having heat-generating elements mounted thereon, for use with one example of conventional ink-jet recorders. In the drawing, reference numeral 1 designates a common electrode; 2 designates heat-generating elements; 3 designates driver elements; 4 designates pre-drivers; 5 designates NAND circuits; 21 designates a 16-bit counter; 22 designates a 64-bit latch; and 23 designates a 64-bit shift register.
In this example, sixty-four heat-generating elements 2 are mounted on the substrate. More precisely, areas for sixty-four heat-generating elements 2 are ensured on the substrate. Therefore, the following cases are implicit in the above-described explanation; namely, where there is ensured only the area at which the heat-generating elements 2 are to be placed, and the heat-generating elements 2 are not actually mounted on that area; where the heat-generating elements have different characteristics and, hence, are not used in ordinary printing operations; and where the heat-generating elements are dummy elements. For example, if a print is produced in several different colors using one substrate, several dummy elements are usually provided between the colors. Based on the previous descriptions, the number of heat-generating elements capable of being provided will be herein referred to as the number of heat-generating elements.
FIG. 34 illustrates a case where sixty-four heat-generating elements are divided into sixteen blocks every four elements and are driven in a separated manner. The sixty-four heat-generating elements are at one end thereof connected to the power source via the common electrode 1, and are at the other end thereof connected to the driver elements 3 respectively. The driver elements 3 can be formed from; e.g., a MOS-FET or a transistor, and drive the heat-generating elements 2. The pre-driver 4 boosts a drive signal for the corresponding heat-generating element 2 and enters the thus-boosted drive signal into the control electrode of the driver element 3; e.g., a gate electrode of a MOS-FET. The NAND circuit 5 receives one split-block drive signal, an ENABLE signal, and a data signal from the 64-bit latch 22. The NAND circuit 5 outputs the drive signal to the pre-driver 4 while the corresponding heat-generating element 2 is selected; while there is data to be printed; and while the NAND circuit 5 has received the ENABLE signal.
The 16-bit counter 21 counts clock pulses and then issues a split-block drive signal. The thus-issued split-block drive signal enters the NAND circuit 5 which corresponds to the block. The 64-bit latch 22 retains print data corresponding to each heat-generating element 2. The 64-bit shift register 23 sequentially retains serially-entered data and transfers the thus-received data to the 64-bit latch 22 in a parallel manner.
In the present example, the 64-bit latch holds 64 items of print data corresponding to the respective heat-generating elements 2. However, for instance, as illustrated in FIG. 5 of the Unexamined Japanese Patent Application Publication No. Hei 6-79873 and in FIG. 5 and others of the Japanese Patent Application No. Hei 6-272375, there is a latch arranged so as to latch only the print data corresponding to one block.
FIG. 35 is a timing chart illustrating one example of operations of the conventional ink-jet recorder. Sixty-four items of print data corresponding to the heat-generating elements 2 previously entered the 64-bit shift register 23 in a serial manner before the first printing operations, are commenced. Subsequently, the 64-bit latch 22 is reset by a DRST signal, and all the print data stored in the 64-bit shift register 23 are transferred to and latched into the 64-bit latch 22 by means of a LCLK signal. The 64-bit latch 22 outputs the thus-received print data to the NAND circuits 5, respectively.
The 16-bit counter 21 is reset by a BRST signal. After the order in which the heat-generating elements are driven has been selected by a BDIR signal, the 16-bit counter 21 counts a BCLK signal and selectively sends the split-block drive signal. According to the timing chart provided in FIG. 35, forward-printing operations are selected when there is a low BDIR signal, whereas reverse-printing operations are selected when there is a high BDIR signal. In response to the first BCLK signal, the 16-bit counter 21 outputs the split-block drive signal, corresponding to the first block, to the first through fourth NAND circuits 5. Of the first through fourth NAND circuits 5, only the NAND circuits 5 that receive print data from the 64-bit latch 22, output a drive signal according to the ENABLE signal, whereby the driver elements 3 are driven via the pre-drivers 4. As a result, of the first through fourth heat-generating elements 2, the heat-generating elements 2 for which there is a print data, permit the flow of an electrical current. Thus, the heat-generating elements 2 are heated. At this time, ink is not squirted during the pre-pulse, only the temperature of the ink is increased as a result of heating operations of the heat-generating elements 2. Bubbles develop in the ink as a result of heating operations of the heat-generating element 2 during the next main pulse, so that ink is squirted and a print is achieved.
The 16-bit counter 21 counts the next BCLK signal and outputs the split-block drive signal corresponding to the second block, to the fifth to eighth NAND circuits 5. Of the fifth through eighth heat-generating elements 2, those heat-generating elements 2 which receive print data, are heated, whence printing operations are carried out. Similarly, blocks of the heat-generating elements are driven in order as far as the 16th block. During the course of drive of the heat-generating elements, the next sixty-four items of print data enter the 64-bit shift register 23.
After drive of the heat-generating elements of the sixteen blocks has been completed, the 16-bit counter 21 is reset by the BRST signal. The direction in which the heat-generating elements are driven is determined by the BDIR signal. In the timing chart provided in FIG. 35, reverse-printing operations are set. The 64-bit latch 22 is reset by the DRST signal, and the print data stored in the 64-bit shift register 23 is latched into the 64-bit latch 22 by an LCLK signal. In the later operations, the heat-generating elements of the blocks are driven in order from the 16th block, and the heat-generating elements of the first block are finally driven. Printing operations are carried out through the repetition of a series of the previously-described operations.
With the foregoing arrangement, if the 16-bit counter 21 is disposed on the substrate having the heat-generating elements 2 mounted thereon, the lateral direction of the substrate is limited as a result of layout of the heat-generating elements 2 which are mounted on top of the substrate. Accordingly, it is necessary to arrange the 16-bit counter 21 in an extremely oblong pattern. Means for driving the heat-generating elements on a block-by-block basis in a time-sharing manner, should preferably have bidirectionality as previously described. Use of; e.g., a binary counter, a Johnson counter, a linear feed-back shift register, or a gray code counter, results in a reduction in the number of gates; however, it is difficult to reduce the area of the layout by routing conductor. For these reasons, it is common to mount the most fundamental counter which uses as many shift registers as there are blocks. In this case, if it is desirable to provide the counter with bidirectionality, it is only necessary to place a selector for reversing the order of shift registers provided before and after the counter, between the shift registers.
In addition to the technique of driving the blocks of the heat-generating elements in a time-sharing manner by utilization of a counter, there is a technique of selecting a block that is driven by decoding a drive signal received from outside of the substrate to a binary code within the substrate. However, the technique of selecting a block that is driven using a binary-decoded signal, requires as many input signal lines for driving purposes as log2 of the number of split blocks. For example, when 25=32 blocks, there are required as many as five input signal lines for block driving purposes.
The number of lines is material in terms of cost and high-density integration of a substrate, and a small circuit scale is desirable in order to reduce the area of a chip and to reduce the heat generated as a result of power consumption. However, if the number of input signal lines is reduced by sharing functions and address lines with one another, a decoding circuit will become necessary, thereby resulting in a larger circuit size. Further, the speed of print processing will decrease as a result of decoding operations. In the case of double pulse driving operations, or in the case of insertion of a pulse for driving other heat-generating elements during the interval between the pre-pulse and the main pulse, it will become more difficult to reduce the number of wires.